Captain Throwback has released a flashable radio update for the 3.17.651.4 radios, which includes the new radios and PRI. This supposedly enables HD Voice and provides better speeds. You’ll need to be S-OFF, as the update has been pieced together into an unsigned, bootloader flashable zip. This means you’ll need to download the package, rename the zip to PJ75IMG, and place it on your SD card. After that, boot into bootloader, and it should prompt you to install the radios automatically.
I just did this, verified that I’m able to make calls, and also see that my 3G download speeds are improved. However, my tower is in the process of an overhaul, so my results are not particularly the results you will see and vary day to day. The radio updates found here also contain no hboot, recovery, or boot.img, so you can theoretically install this without worrying about making a nandroid backup.
One thing to be wary of, though, is some ROMs do not play nice with radio changes. If you’re not the adventurous type, give this a day or so and let the other people be the guinea pigs.
A fully stock, rooted 3.17.651.4 is expected out fairly soon, so we should see some new Sense-based ROMs being deployed tonight. We also may hear the screaming of people who have updated their radios and found their ROMs no longer works properly – but hopefully that won’t be the case and we’ll have an actual update that doesn’t break something else, which could be a first from HTC.